Add toggle switch boolean fields

[CelinaKellinghaus]

Boolean form fields (optimize_cap, dispatchable, renewable_asset) are now displayed as toggle switches instead of yes/no dropdowns.
A new "Settings" section was added above the economical parameters to group these fields together.

Note:
Toggle styles in _forms.scss are commented out and not functional yet.
Styles are currently applied inline in the widget.

Fixes #483.

[paulapreuss]

@CelinaKellinghaus This looks great so far! I have no complaints about it :-)

I couldn't really reproduce any issue with moving the code to the scss file - I simply uncommented the code in the file and removed the <style> block from the template and it was working just fine. Then I updated the main.css file by running collectstatic and copy-pasting the updated main.css in cdn_static_root (which was compiled using the scss files) to the one in static.